Longitudinal Evaluation of Residual Cortical and Subcortical Motor Evoked Potentials in Spinal Cord Injured Rats

Abstract

We have applied transcranial electrical stimulation to rats with spinal cord injury and selectively tested the motor evoked potentials (MEPs) conveyed by descending motor pathways with cortical and subcortical origin. MEPs were elicited by electrical stimulation to the brain and recorded on the tibialis anterior muscles. Stimulation parameters were characterized and changes in MEP responses tested in uninjured rats, in rats with mild or moderate contusion, and in animals with complete transection of the spinal cord. All injuries were located at the T8 vertebral level. Two peaks, termed N1 and N2, were obtained when changing from single pulse stimulation to trains of 9 pulses at 9 Hz. Selective injuries to the brain or spinal cord funiculi evidenced the subcortical origin of N1 and the cortical origin of N2. Animals with mild contusion showed small behavioral deficits and abolished N1 but maintained small amplitude N2 MEPs. Substantial motor deficits developed in rats with moderate contusion, and these rats had completely eliminated N1 and N2 MEPs. Animals with complete cord transection had abolished N1 and N2 and showed severe impairment of locomotion. The results indicate the reliability of MEP testing to longitudinally evaluate over time the degree of impairment of cortical and subcortical spinal pathways after spinal cord injuries of different severity.

Low frequency pulsed electromagnetic field promotes the recovery of neurological function after spinal cord injury in rats

“…These results preliminarily indicated that LFPEMF had a therapeutic effect on rats after SCI. To further investigate the therapeutic effect of LFPEMF, tcMMEPs, a widely used method to evaluate the recovery of electrophysiological function after SCI, were recorded weekly after surgery. Compared to the SCI group, tcMMEP latencies and amplitudes were significantly improved in the LFPEMF group from 2 to 8 weeks after surgery, which further suggested that LFPEMF could promote the recovery of neurological function in rats after SCI.…”

“…The measurement of tcMMEPs, a form of MEP, involves a pair of Magstim 200 stimulators attached to a 50 mm diameter transducer coil. This apparatus has been widely used to evaluate the recovery of electrophysiological function after SCI, and the detection method has been described in our previous study . In brief, the transducer was positioned over the skull of the rat, and the single pin electrodes used to record EMG responses were placed into the hindlimb tibialis anterior muscle and gastrocnemius muscle of the rat.…”

Increased threshold of short-latency motor evoked potentials in transgenic mice expressing Channelrhodopsin-2

“…In contrast, the long-latency MEPs appear as a set of polyphasic waves of variable latency (15–22 ms), with a prominent peak at latency around 15 ms and mainly involves corticospinal tracts. Transecting the motor cortex or dorsal corticospinal tract abolishes most of the long-latency MEPs but spares the short-latency MEPs [18–20]. Our result of reduced amplitude of short-latency MEPs indicates reduced excitability of reticulospinal tract in ChR2-YFP transgenic mice.…”

“…The first is a short-latency and high amplitude (~ 5 ms) response; the second is a long-latency (~15 ms), polyphasic wave that involves motor cortex and corticospinal tract [18, 19]. To specifically evaluate the long-latency MEPs, mouse motor cortex was electrically stimulated via an implanted screw.…”

In vivo conversion of rat astrocytes into neuronal cells through neural stem cells in injured spinal cord with a single zinc-finger transcription factor

“…We stimulated the left motor cortex and recorded the right tibia muscle. In intact recordings (2 days before SCI), every excitation elicited two separate waves, N1 MEPs and N2 MEPs [41]. N1 MEPs were single transcranial electrical pulses that were evoked with a short latency and recorded in the tibia anterior muscles in all of the animals that we tested.…”